Here we're going to add two functions to support alpha transparency on a texture. First there's setAlpha which will function much like setColor did in the color modulation tutorial.
There's also setBlendMode which will control how the texture is blended. In order to get blending to work properly, you must set the blend mode on the texture. We'll cover this in
detail later.

Here in the texture loading function we're loading the front texture we're going to alpha blend and a background texture. As the front texture gets more transparent, we'll be able to
see more of the back texture. As you can see in the code, after we load the front texture successfully we set the
SDL BlendMode to blend so blending is enabled. Since the background isn't going to be transparent, we don't
have to set the blending on it.

Now how does alpha work? Alpha is opacity, and the lower the opacity the more we can see through it. Like red, green, or blue color components it goes from 0 to 255 when modulating
it. The best way to understand it is with some examples. Say if we had the front image on a white background.

At the end of the main loop we do our rendering. After clearing the screen we render the background first and then we render the front modulated texture over it. Right before
rendering the front texture, we set its alpha value. Try increasing/decreasing the alpha value to see how transparency affects the rendering.